JSP 中Hibernate实现映射枚举类型
问题：
Java BO类Gender是枚举类型，想在数据库中存成字符串格式，如何编写hbm.xml？
public enum Gender{
UNKNOWN("Unknown"), MALE("Male"), FEMALE("Female");
private String key;
private Gender(final String key) {
this.key = key;
}
public getGender(String key) {
for (Gender gender : Gender.values()) {
if (key.euqals(gender.getKey())) return gender;
}
throw new NoSuchElementException(key);
}
}
使用UserType：
public class GenderUserType implements UserType {
private static int[] typeList = {
Types.VARCHAR}
;
/* * Return the SQL type codes for the columns mapped by this type. * The codes are defined on <tt>java.sql.Types</tt>. */ /**设置和Gender类的sex属性对应的字段的SQL类型 */ public int[] sqlTypes() {
return typeList;
}
/*The class returned by <tt>nullSafeGet()</tt>.*/ /** 设置GenderUserType所映射的Java类：Gender类 */ public Class returnedClass() {
return Gender.class;
}
/** 指明Gender类是不可变类 */ public boolean isMutable() {
return false;
}
/* * Return a deep copy of the persistent state, stopping at entities and at * collections. It is not necessary to copy immutable objects, or null * values, in which case it is safe to simply return the argument. */ /** 返回Gender对象的快照，由于Gender类是不可变类， 因此直接将参数代表的Gender对象返回 */ public Object deepCopy(Object value) {
return (Gender)value;
}
/** 比较一个Gender对象是否和它的快照相同 */ public boolean equals(Object x, Object y) {
//由于内存中只可能有两个静态常量Gender实例， //因此可以直接按内存地址比较 return (x == y);
}
public int hashCode(Object x){
return x.hashCode();
}
/* * Retrieve an instance of the mapped class from a JDBC resultset. Implementors * should handle possibility of null values. */ /** 从JDBC ResultSet中读取key，然后返回相应的Gender实例 */ public Object nullSafeGet(ResultSet rs, String[] names, Object owner) throws HibernateException, SQLException{
//从ResultSet中读取key String sex = (String) Hibernate.STRING.nullSafeGet(rs, names[0]);
if (sex == null) {
return null;
}
//按照性别查找匹配的Gender实例 try {
return Gender.getGender(sex);
}
catch (java.util.NoSuchElementException e) {
throw new HibernateException("Bad Gender value: " + sex, e);
}
}
/* * Write an instance of the mapped class to a prepared statement. Implementors * should handle possibility of null values. * A multi-column type should be written to parameters starting from <tt>index</tt>. */ /** 把Gender对象的key属性添加到JDBC PreparedStatement中 */ public void nullSafeSet(PreparedStatement st, Object value, int index) throws HibernateException, SQLException{
String sex = null;
if (value != null) sex = ((Gender)value).getKey();
Hibernate.String.nullSafeSet(st, sex, index);
}
/* * Reconstruct an object from the cacheable representation. At the very least this * method should perform a deep copy if the type is mutable. (optional operation) */ public Object assemble(Serializable cached, Object owner){
return cached;
}
/* * Transform the object into its cacheable representation. At the very least this * method should perform a deep copy if the type is mutable. That may not be enough * for some implementations, however;
for example, associations must be cached as * identifier values. (optional operation) */ public Serializable disassemble(Object value) {
return (Serializable)value;
}
/* * During merge, replace the existing (target) value in the entity we are merging to * with a new (original) value from the detached entity we are merging. For immutable * objects, or null values, it is safe to simply return the first parameter. For * mutable objects, it is safe to return a copy of the first parameter. For objects * with component values, it might make sense to recursively replace component values. */ public Object replace(Object original, Object target, Object owner){
return original;
}
}
然后再hbm.xml中定义映射关系：
<hibernate-mapping package="" default-lazy="true" default-cascade="save-update,merge,persist"> <typedef name="Gender" class="com.alpha.hibernate.GenderUserType"> <property name="gender" type="Gender"> <column name="GENDER" not-null="true"> </column> </property>
延伸：
为每个枚举类型定义一个UserType是比较麻烦的，可以定义一个抽象类。
例如扩展下例即可适用于所有保存为index的枚举类型
public abstract class OrdinalEnumUserType<E extends Enum<E>> implements UserType {
protected Class<E> clazz;
protected OrdinalEnumUserType(Class<E> clazz) {
this.clazz = clazz;
}
private static final int[] SQL_TYPES = {
Types.NUMERIC}
;
public int[] sqlTypes() {
return SQL_TYPES;
}
public Class<?> returnedClass() {
return clazz;
}
public E nullSafeGet(ResultSet resultSet, String[] names, Object owner) throws HibernateException, SQLException {
//Hibernate.STRING.nullSafeGet(rs, names[0]) int index = resultSet.getInt(names[0]);
E result = null;
if (!resultSet.wasNull()) {
result = clazz.getEnumConstants()[index];
}
return result;
}
public void nullSafeSet(PreparedStatement preparedStatement, Object value,int index) throws HibernateException, SQLException {
if (null == value) {
preparedStatement.setNull(index, Types.NUMERIC);
}
else {
//Hibernate.String.nullSafeSet(st, sex, index);
preparedStatement.setInt(index, ((E)value).ordinal());
}
}
public Object deepCopy(Object value) throws HibernateException{
return value;
}
public boolean isMutable() {
return false;
}
public Object assemble(Serializable cached, Object owner) throws HibernateException {
return cached;
}
public Serializable disassemble(Object value) throws HibernateException {
return (Serializable)value;
}
public Object replace(Object original, Object target, Object owner) throws HibernateException {
return original;
}
public int hashCode(Object x) throws HibernateException {
return x.hashCode();
}
public boolean equals(Object x, Object y) throws HibernateException {
if (x == y) return true;
if (null == x || null == y) return false;
return x.equals(y);
}
}
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